Outlook ANywhere & XP Password issue ?

I have a few users still on XP pro.. For some reason and it seems to happen randomly when using outlook anywhere they will get prompted for a password, and it does not work or let them back in .. just keeps on prompting for credentials.. the only way I have been able to resolve is delete the outlook profile and than re create but than after a time it starts again..
I tried unchecking use encryption box in the profile settings.. I can not seem to find a fix for this anywhere..

IP V6 is off on the exchange server..
I am wondering if there is a seting in IIS ?

ok looking at some posts... I want to make sure i understand this fully..
outside domain is for example... mail.com
intenal mail.lan
If i run get-outlookprovider cmdle..
i get this
[PS] C:\Windows\system32>Get-OutlookProvider

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